Slip Uno adapters are made to fit directly over a plastic lamp socket found on lamps usually purchased at places like IKEA this adapter and harp attached to it. Then it will allow you to use nearly any replacement shade on that lamp. This is meant to be an alternative to the lampshade which has fitter already attached to it. The opening on this adapter is 1 9/16". A plastic washer (ring) is needed to hold the adapter tightly in place. please note there are two sizes of this fitter this one and one with a smaller hole if thats the one you need.